The problem is that he is still set as the main teacher through Staff Groups on the SIMS Employee details page, so no matter what I do to the lesson teachers through Edit Lesson Staff and Rooms, he still seems to 'own' the class. I have completely removed him from all timetabled lessons using Edit Lesson Staff and Rooms for the whole of history, but SIMS still seems to regard him as the Class Teacher for the purposes of the tag in Individual Reports, so still puts his name in if I set the effective date to a date he was still employed, or to a blank if I set the effective date to today